Carbinol acetals, rearrangement

Ethynyl carbinols rearrange to conjugated unsaturated aldehydes. Copper or silver salts cataly2e isomeri2ation of the acetate to an aHenic acetate, which can be hydroly2ed to an unsaturated aldehyde (204). 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Synthetic methods for 2(5jF/)-furanones have been developed in the preparation of cardenolides (65MI31200). The ketone (171) when reacted with lithium ethoxyacetylide gives the carbinol (172) which undergoes acid catalyzed rearrangement to the a,/3-unsaturated ester (173). Allylic oxidation of (173) with selenium dioxide under mild conditions gives digitoxigenin acetate (174) (Scheme 38). 

The diazepinol (40) is readily obtained from ketone (10) with sodium borohydride and is converted back into 10 with A -bromoacetamide or by Oppenauer oxidation.32 In a similar manner 32 and the AT-acetyl derivative of 10 can be reduced to carbinols. Acylation of 40 or treatment of the reduction product of 32 with acetic acid gave the trans-annular oxide (41). The carbinol (40), the acetyl carbinol from 10, the oxide (41), and the diacetyl analog of 41 all undergo rearrangement with mineral acid to give the four furfurylhydrazines (42).32... 

Oxidation of the carbinol (4) with periodate does not give the expected iro-epoxy compound but the benzaldehyde acetal of 3,5-di-t-butylcatechol (5). This oxidative rearrangement is apparently limited to o-hydroxy-substituted diaiyl- and triaryl-carbinols. ... 

Diquinolylmethanes are oxidized to diquinolylketones (13) by air-02, H2O2, or CrOa in acetic acid. - The ketones (13) can also be prepared by condensation of the diquinolylmethanes with p-nitroso-dimethylaniline, followed by hydrolysis with sulfuric acid. The ketoximes (14) undergo the Beckmann rearrangement, with PCI 5 in ether, to give amides (15). On oxidation, triquinolylmethanes give the corresponding carbinols. ... 

Thiosemicarbazones of 3-, 4-, and 5-methylisoquinoline-1-carboxaldehyde have also been synthesized [18] to assist in a definition of molecular dimensions compatible with biological activity. The syntheses of the methyl-substituted derivatives were accomplished by rearrangement of the N-oxides of 1,3-, and 1,4-dimethylisoquinoline with acetic anhydride followed by acid hydrolysis of the ester and subsequent oxidation of the carbinol with manganese dioxide. However, 1,5-dimethylisoquinoline (77) was selectively oxidized with selenium dioxide to the corresponding 1 [Pg.337]

Mulzer and Mohr used a glycolate Claisen to establish the C6, C7 stereocenters in an asymmetric synthesis of the asteltoxin Ws-tetrahydrofuran fragment (Scheme 4.127) [121]. Rearrangement occurred via the expected Z-silyl ketene acetal and chair transition state to afford the adjacent carbinol and 4° carbon stereocenters. The high stereoselectivity of the rearrangement using a tetrasubsti-tuted aUyUc alkene is noteworthy. 

When divinyl carbinols are heated with dimethylacetamide dimethyl acetal (4), the less substituted and less electron-rich double bond engages in the rearrangement (Scheme 7.13, Eqs. 1 and 2) [29]. Vinyl-propargyl carbinols were found to rearrange with preferential participation of the double bond (Eq. 3) [30]. For another case of a highly regjoselective Eschenmoser-Qaisen rearrangement see Scheme 7.16, Eq.4[31]. 

A related [l,2]-rearrangement was described by Schlenk and Bergman in 1928. As shown below, reduction of benzophenone dimethyl acetal (6) with metallic sodium led to the formation of diphenyl methyl carbinol (8), presumably via intermediate organosodium species 7. ... 

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